A great variety of engines, which convert fluid pressure into rotary motion of a drive shaft, and a great variety of pumps, which convert the rotary motion of a drive shaft into fluid pressure, are known. Many of these devices employ one or more reciprocating pistons to achieve the power conversion. Reciprocating pistons, however, have a number of disadvantages. They are, for example, characteristically bulky, prone to vibration problems and require a large amount of mechanical components, all of which tend to unnecessarily limit the rotational speed of the drive shaft and make the power conversion inefficient. Frictional losses are high.
In an effort to address the disadvantages stemming from reciprocating pistons, engines and pumps have been developed which use non-reciprocating, or rotary, members or a combination of reciprocating and rotary members instead of pistons. By way of example, forms of such devices are described in U.S. Pat. No. 4,174,195 to Lassota and U.S. Pat. No. 1,579,010 to Levine.
Such arrangements can result in a reduction in the size and bulk of the device. This tends to increase the efficiency of power conversion, since the device is now somewhat more light in weight relative to the amount of power or fluid pressure output. Even these devices, however, have significant drawbacks.
Relative to the amount of power or fluid pressure output, they are, for example, still bulky and heavy and rely upon large numbers of moving mechanical parts. They are, therefore, inefficient from a power conversion standpoint, prone to succumb to wear sooner than anticipated, and are costly to manufacture. Their size and bulk also limit the environments in which they can be utilized. Further inefficiency in power conversion also stems from vibration problems and the fact that fluid pressure acts upon relatively small surface areas of the members which are used in the devices. These devices are often not effectively reversible. That is, they cannot effectively operate alternatively as engines or as vacuum pumps.
Accordingly, it should be appreciated that there has existed a definite need for a power conversion device which is relatively inexpensive to manufacture, which experiences less vibration, which, relative to the amount of power or fluid pressure output, is less bulky, lightweight and has fewer moving parts, and which is capable of more efficiently converting between fluid pressure and rotary motion.